Priority codes are only useful if the clock starts when the user reports, not when someone accepts the job.
Reactive performance reporting is easy to flatter. If the timer starts on acceptance rather than on the original report, the figure describes the helpdesk rather than the user's experience.
Priority codes should be defined against consequence — safety, security, business interruption, comfort — and agreed in writing before mobilisation, so triage is not a judgement call at the point of the call.
Jobs that are attended but not resolved need their own category. Counting a first visit as a fix is the single most common reason a report and a building disagree.